Bursting of rigid bubbles

We propose here a fluid dynamics video relating the bursting of soap rigid films.Comment: 4 pages and 2 videos included for the Gallery of Fluid Motion 201

Holes and cracks in rigid foam films

The classical problem of foam film rupture dynamics has been investigated when surfaces exhibit very high rigidity due to the presence of specific surfactants. Two new features are reported. First a strong deviation to the well-known Taylor-Culick law is observed. Then, crack-like patterns can be visualized in the film; these patterns are shown to appear at a well defined deformation. The key role of surface active material on these features is quantitatively investigated, pointing the importance of surface elasticity to describe these fast dynamical processes, and thus providing an alternative tool to characterize surface elasticity in conditions extremely far from equilibrium. The origin of the cracks and their consequences on film rupturing dynamics are also discussed

How Topological Rearrangements and Liquid Fraction Control Liquid Foam Stability

International audienceThe stability of foam is investigated experimentally through coalescence events. Instability (coalescence) occurs when the system is submitted to external perturbations (T1) and when the liquid amount in the film network is below a critical value. Microscopically, transient thick films are observed during film rearrangements. Film rupture, with coalescence and eventual collapse of the foam, occurs when the available local liquid amount is too small for transient films to be formed. Similar experiments and results are shown in the two-bubble case

the practice and usefulness of bone marrow examinations in a cohort of human immunodeficiency virus infected children in South Africa: a descriptive study

INTRODUCTION: Bone marrow examination (BME) is performed in Human Immunodeficiency Virus-infected (HIV+) children with haematologic abnormalities to exclude specific disease (SD). AIMS: To describe the: (1) indications for BME , (2) utility of BME to diagnose SD, (3) patient characteristics associated with SD or non-specific disease (NSD). METHODS: Design: Retrospective review. Definitions: SD: BME positive for opportunistic infection (OI) or HIV-related malignancy. NSD: HIV-related changes only. RESULTS: Eighty six BME’s were done. Suspected SD in 56/86(65.1%) was the most common clinical indication. Bicytopaenia(n=32) and isolated cytopaenia(n=31) were the most common haematologic indications. NSD 48/86 (55.8%) was a more common finding than SD 32/86 (37.2%). Granulomas, pure red cell aplasia and malignancy were the SD identified. Pre- highly active antiretroviral therapy (HAART), advanced stage, and not being virally suppressed were significantly associated with NSD. CONCLUSION: The yield of SD (37.2%) on BME is comparable to adult studies. HAART should be instituted before BME as NSD will be the most likely finding

Patients with both langerhans cell histiocytosis and crohn’s disease highlight a common role of interleukin-23

Aim: To present the first case series of patients with Langerhans cell histiocytosis (LCH) also affected by Crohn's disease (CD), both of which are granulomatous diseases, and in LCH investigate the role of interleukin (IL)-23, which is a well-described disease mediator in CD. Methods: A case series of three patients with LCH and CD were described; a cohort of LCH patients (n = 55) as well as controls (n = 55) were analysed for circulating IL-23 levels; and the relation between the percentage of LCH cells in lesions and circulating IL-23 levels was analysed in seven LCH patients. Results: Differential diagnostic challenges for these two granulomatous diseases were highlighted in the case series, and it took up to 3 years to diagnose CD. Elevated IL-23 levels were found in LCH patients. The amount of lesional LCH cells correlated with the levels of circulating IL-23. Conclusion: Both CD and LCH should be considered in patients with inflammatory gastrointestinal involvement. The IL-23 pathway is a common immunological trait between these two granulomatous diseases. ©2020 The Authors. Acta Paediatrica published by John Wiley & Sons Ltd on behalf of Foundation Acta Paediatrica. ***Please note that there are multiple authors for this article therefore only the name of the first 5 including Federation University Australia affiliate “Jenée Mitchell” is provided in this record**

Numerical simulation of spreading drops

We consider a liquid drop that spreads on a wettable surface. Different time evolutions have been observed for the base radius r depending of the relative role played by inertia, viscosity, surface tension and the wetting condition. Numerical simulations were performed to discuss the relative effect of these parameters on the spreading described by the evolution of the base radius r(t) and the spreading time tS. Different power law evolutions r(t) ∝ tⁿ have been observed when varying the parameters. At the early stage of the spreading, the power law t½ (n = 1/2) is observed as long as capillarity is balanced by inertia at the contact line. When increasing the viscosity contribution, the exponent n is found to increase despite the increase of the spreading time. The effect of the surface wettability is observed for liquids more viscous than water. For a small contact angle, the power law t½ is then followed by the famous Tanner law t1/10 once the drop shape has reached a spherical cap

Level-set simulations of a 2D topological rearrangement in a bubble assembly: effects of surfactant properties

International audienceA liquid foam is a dispersion of gas bubbles in a liquid matrix containing surface active agents. Their flow involves the relative motion of bubbles, which switches neighbours during a so-called topological rearrangement of type 1 (T1). The dynamics of T1 events, as well as foam rheology, have been extensively studied, and experimental results point to the key role played by surfactants in these processes. However, the complex and multiscale nature of the system has so far impeded a complete understanding of the mechanisms at stake. In this work, we investigate numerically the effect of surfactants on the rheological response of a 2D sheared bubble cluster. To do so, a level-set method previously employed for simulating two-phase flow has been extended to include the effects of the surfactants. The dynamical processes of the surfactants-diffusion in the liquid and along the interface, adsorption/desorption at the interface-and their coupling with the flow-surfactant advection and Laplace and Marangoni stresses at the interface-are all taken into account explicitly. Through a systematic study in Biot, capillary and Péclet numbers which characterise the surfactant properties in the simulation, we find that the presence of surfactants can affect the liquid/gas hydrodynamic boundary condition (from a rigid-like situation to a mobile one), which modifies the nature of the flow in the volume from a purely extensional situation to a shear. Furthermore, the work done by surface tension (the 2D analogue of the work by pressure forces), resulting from surfactant and interface dynamics, can be interpreted as an effective dissipation, which reaches a maximum for Péclet number of order unity. Our results, obtained at high liquid fraction, should provide a reference point, to which experiments and models of T1 dynamics and foam rheology can be compared